1. Field of the Invention
The present invention relates to an image pickup apparatus and method, and more particularly to an image pickup apparatus and method in which signals of pixels in an image pickup area are read out through addition thereof.
2. Related Background Art
A method is known by which a particular image pickup area is displayed with being magnified on a display device by using a smaller number of pixels than the display device. An image pickup apparatus using this method will be described.
FIG. 1 is a schematic diagram showing the structure of an image pickup apparatus. This image pickup apparatus is constituted of photoelectric conversion element 101, vertical transfer paths 102, storage units 103, a horizontal transfer path 104, a signal charge detector 105, and an output unit 106 provided on the opposite side of the horizontal transfer path 104. Arrows indicate a conventional transfer direction of signal charges.
FIGS. 2A to 2K show typical pulse waveforms for driving the image pickup apparatus having the storage units. FIG. 2A shows a composite blanking signal, FIGS. 2B, 2C, 2D and 2E show four-phase clock signals to be applied to the vertical transfer paths 102, having vertical transfer pulse waveforms (hereinafter described as φVA1, φVA2, φVA3, φVA4) to be applied to gates VA1, VA2, VA3 and VA4. FIGS. 2F, 2G, 2H and 2I show four-phase clock signals to be applied to the storage units 103, having vertical transfer pulse waveforms (hereinafter described as φVB1, φVB2, φVB3, φVB4) to be applied to gates VB1, VB2, VB3 and VB4. FIG. 2J shows a discrimination signal (hereinafter described as pre-blanking signal) for discriminating effective CCD output signals. FIG. 2K shows a transfer pulse (hereinafter described as horizontal transfer pulse) to be used for transferring signal charges in the horizontal transfer path 104 to the signal charge detector 105.
Next, a conventional method of driving an image pickup apparatus will be described with reference to FIG. 1 and FIGS. 2A to 2K.
During a vertical blanking period A3, accumulated charges are transferred from the photoelectric conversion element 101 to the vertical transfer paths 102 in response to charge pulses C3 shown in FIGS. 2B to 2E. Next, the charges are transferred from the vertical transfer paths 102 to the storage units 103 by a transfer amount corresponding to the number of stages of each storage unit in response to vertical high speed transfer pulses F3. Next, during an image scanning period B3, the charges are transferred to the horizontal transfer path 104 during each horizontal period G3 by applying vertical transfer pulses I3 to the storage units 103. At the same time, during each horizontal period G3, i.e., at each timing of the vertical transfer pulses I3, signal charges on the horizontal transfer path 104 are output from the signal charge detector 105 by applying horizontal transfer pulses H3 to the horizontal transfer path 104. The horizontal transfer pulses have a frequency capable of transferring the signal charges of one horizontal scan.
From the start of the vertical blanking period A3 until application of the charge pulses C3, vertical high speed transfer pulses D3 are applied to the vertical transfer paths 102 to drain unnecessary charges in the vertical transfer paths 102 from the output unit 106 provided on the opposite side of the horizontal transfer path 104.
With this drive method, the vertical transfer paths 102 and storage units 103 can operate independently and an electronic shutter speed of 1/60 second to 1/1600 second can be attained.
Next, with reference to pulse waveforms shown in FIGS. 3A to 3K, a method will be described by which an image pickup apparatus with storage units is driven to display a partial image area magnified to have twofold vertical and horizontal lengths and a fourfold area ratio. Pulse waveforms shown in FIGS. 3A to 3K are used for magnifying a central area of an image (this magnification operation is described hereinafter as an electronic zoom operation). FIG. 3A shows a composite blanking signal, FIGS. 3B, 3C, 3D and 3E show four-phase clock signals to be applied to the vertical transfer paths 102, respectively represented by φVA1, φVA2, φVA3, φVA4. FIGS. 3F, 3G, 3H and 3I show four-phase clock signals to be applied to the storage units, respectively represented by φVB1, φVB2, φVB3, φVB4. FIG. 3J shows a pe-blanking signal, and FIG. 3K shows horizontal transfer pulse waveforms.
During a vertical blanking period A4, accumulated charges are transferred from the photoelectric conversion element 101 to the vertical transfer paths 102 in response to charge pulses C4. Next, the charges are transferred from the vertical transfer paths 102 to the storage units 103 by a transfer amount corresponding to the number of stages of each storage unit in response to vertical high speed transfer pulses E4. In the storage units 103, the charges are transferred by a transfer amount more than the stages by one fourth the number of stages of each storage unit in response to vertical high speed transfer pulses F4 to drain the charges from the horizontal transfer path 104 and signal charge detector 105. Next, during an image scanning period B4, charges left in the storage units 103 corresponding to three fourths the number of stages are transferred to the horizontal transfer path 104 by applying a vertical transfer pulse 14 to the storage units 103 at timing generally the center of each horizontal scan period and at every second horizontal periods. At the same time, during a period between two vertical transfer pulses, signal charges on the horizontal transfer path 104 are output from the signal charge detector 105 by applying horizontal transfer pulses H4 to the horizontal transfer path 104, the horizontal transfer pulses having a frequency capable of transferring the signal charges of one horizontal scan. With these operations, pixel signals of the photoelectric conversion element 101 in an area from about one fourth to three fourths of the photoelectric conversion element, viewed from the side of the storage units 103, i.e., pixel signals in the central area, are magnified and output during one image scanning period. At the end of the image scanning period B4, signal charges in the photoelectric conversion element in an area of one fourth, located at the opposite side of the storage units 103 are left in a partial area of the storage units 103. These remaining signal charges are transferred to the horizontal transfer path 104 and drained from the signal detector 105 in response to high speed transfer pulses J4 applied at the start period of the next vertical blanking period A4.
Next, the detected signal charges are subjected to a blanking process by a signal processing circuit by using the blanking signal to delay one horizontal scanning period and interpolate the blank area. In this manner, the image magnified two times in horizontal and vertical directions can be displayed in the whole monitor area.
In the above-description, although the central area of an image is magnified, the area to be magnified may be set as desired.
With the above-described process, however, for example, if one fourth the image pickup area is to be displayed in the whole monitor area, the resolution is halved in both vertical and horizontal directions.